Most of the time when people make this accusation, it's because they don't understand the law. For example, the UK 2010 Equality Act states that if a nonprofit's "aim is to tackle a particular disadvantage faced by people who share a protected characteristic" then they are allowed to limit their scope only to people who share that characteristic. Django Girls events, even when limited to only women, do not break the law, any more than women's only hacker schools like Hackbright or App Camp for Girls do. Furthermore, our events are free, and might be best likened to a PyLadies educational meetup.
We recommend you either ignore people who are accusing you of being discriminatory or of breaking the law, or send them one of the links in the response to the above question, "Isn't Django Girls sexist?" If you feel harassed, or are not sure how to respond, reach out to us as firstname.lastname@example.org and we would be glad to support you however we can.